linux-kernel - Re: [PATCH] [RFC] brk randomization: compute RLIMIT_DATA properly (was Re: x86: randomize brk() and RLIMIT

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Message-ID: <Pine.LNX.4.64.0710261414030.18815@twin.jikos.cz>
Date:	Fri, 26 Oct 2007 14:16:21 +0200 (CEST)
From:	Jiri Kosina <jikos@...os.cz>
To:	Hugh Dickins <hugh@...itas.com>,
	Andrew Morton <akpm@...ux-foundation.org>
cc:	Sami Farin <safari-kernel@...ari.iki.fi>,
	Linux kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH] [RFC] brk randomization: compute RLIMIT_DATA properly
 (was Re: x86: randomize brk() and RLIMIT_DATA)

On Fri, 26 Oct 2007, Hugh Dickins wrote:

> > -	if (rlim < RLIM_INFINITY && brk - mm->start_data > rlim)
> > +	if (rlim < RLIM_INFINITY && brk - mm->start_data -
> > +			(mm->start_brk - mm->end_data) > rlim)
> I find the order in that test mysterious.

I agree that the order you proposed is easier to understand on the first 
sight.


From: Jiri Kosina <jkosina@...e.cz>

brk randomization: compute RLIMIT_DATA properly

In cases of heap area placed at randomly-generated offset from
mm->end_data (arch_randomize_brk()), we need to subtract the value of the
offset for setrlimit(RLIMIT_DATA) to work properly -- otherwise we count
the unoccupied memory between mm->end_data and mm->start_brk as occupied.

Signed-off-by: Jiri Kosina <jkosina@...e.cz>

diff --git a/mm/mmap.c b/mm/mmap.c
index facc1a7..673ac7d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -251,7 +251,8 @@ asmlinkage unsigned long sys_brk(unsigned long brk)
 	 * not page aligned -Ram Gupta
 	 */
 	rlim = current->signal->rlim[RLIMIT_DATA].rlim_cur;
-	if (rlim < RLIM_INFINITY && brk - mm->start_data > rlim)
+	if (rlim < RLIM_INFINITY && (brk - mm->start_brk) +
+			(mm->end_data - mm->start_data) > rlim)
 		goto out;
 
 	newbrk = PAGE_ALIGN(brk);
-
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